Passwordless ssh connection from Windows - linux

Question

How can I create an ssh key from Windows and install it on a Linux host using OpenSSH to log in without a password for each connection?

Answer 1

CREATE AND INSTALL SSH KEY
First of all, we need to create a new key in the Windows pc (where we start the connection) using:
ssh-keygen -t rsa
Don't change the default path or remember where you saved the key, it will be used for the next command.
Press enter another two times to avoid using a passphrase (if you don't want it).
After that, if you haven't change the default path, the key will be created into {USERPROFILE}\.ssh\id_rsa.pub.
Now, you can usually use the command ssh-copy-id for installing the key on the remote host, but unfortunately this command is not available on Windows, so we have to install it using this command:
type $env:USERPROFILE\.ssh\id_rsa.pub | ssh {REMOTE_HOST} "cat >> .ssh/authorized_keys"
or if your key is not in the default path:
type {RSA_KEY_PATH} | ssh {REMOTE_HOST} "cat >> .ssh/authorized_keys"
and replace the {RSA_KEY_PATH} with your RSA path.
Replace {REMOTE_HOST} with the remote host IP/Name (like pi#192.168.0.1), launch the command, insert the password if required, and the work is done!
IMPORTANT!
SETTING UP .ssh FOLDER
If the ~/.ssh folder is not existing in your remote host, you need to configure them, this is usually done by the command ssh-copy-id, but we can not access to this power from Windows!
You need to connect to the remote host in ssh and create the .ssh directory and the authorized_keys file for the first time:
ssh {REMOTE_HOST}
Create the .ssh directory:
mkdir ~/.ssh
Set the right permissions:
chmod 700 ~/.ssh
Create the authorized_keys file:
touch ~/.ssh/authorized_keys
Set the right permissions:
chmod 600 ~/.ssh/authorized_keys
NOTE
The authorized_keys is not a folder, if you try to create it using mkdir, the SSH connection passwordless will not work, and if you debug the ssh on the host, you will notice an error/log similar to:
~/.ssh/authorized_keys is not a key file.
ADD YOUR SSH KEY ON YOUR AGENT
Run those two lines on your Windows pc to add the created key on your cmd/powershell:
ssh-agent $SHELL
ssh-add